In the foundry industry, one of the procedures used for making metal parts is by sand casting. In sand casting, disposable molds and cores are fabricated with a mixture of sand and an organic or inorganic binder. The binder is usually used to strengthen the cores, which are the most fragile part of the mold assembly.
One of the fabrication processes used in sand casting is the no-bake process. In this process a liquid curing agent is mixed with the sand and binder to cure the mixture. Generally, the foundry shapes are large and several minutes of worktime is needed for shaping.
A binder commonly used in the no-bake fabrication process is a polyurethane binder derived from curing a polyurethane-forming binder composition with a liquid tertiary amine catalyst. The polyurethane-forming binder composition usually consists of a phenolic resin component and polyisocyanate hardener component. Both the phenolic resin component and the polyisocyanate component typically contain substantial amounts of solvents, i.e. 20 to 40 percent by weight. Although solvent selection depends upon the goals of the formulator and can require a great deal of experimentation to optimize a formulation, esters, aromatics, and non polar solvents are generally used as the solvents.
U.S. Pat. No. 3,676,392 describes a no-bake binder which has been successfully used on a commercial scale. Such polyurethane-forming binder compositions, used in the no-bake process, have proven satisfactory for casting such metals as iron or steel which are normally cast at temperatures exceeding about 2500 degrees Fahrenheit.